[Mageofdancingdr]

I'm gonna take a shot at this and propose what I think may be a better system. Borrowed nearly directly from the swiss rounds of a Magic: the Gathering tournament:
Rank is based on match points. you get 3 points for winning, 1 point for tying, and 0 points for losing.
The first tiebreaker is your opponent's match points. this summed amongst all opponents in alliances against you (counting teams once for each time they faced against you).
The second tiebreaker is your allies' match points (low being better than high. once again, counting teams once for each time you allied with them).
Third tiebreakers would be whatever endgame score is appropriate for the game, and fourth is random.

By tie-breaking off of record instead of points teams no longer have any reason to score for others, but still rewards teams for fighting against harder opponents.

I believe the scoring system is not the place to discourage defense, however I would consider a tiebreaker based on a highest average points scored, but throwing out the top and bottom scores as outliers.